Brake booster



R. C. RIKE BRAKE BOOSTER Nov. 21, 1961 3 Sheets-Sheet 1 Filed Nov. 27, 1959 INVENTOR. Richard 6. R/lre BY Q 4 Add? His Ail may Nov. 21, 1961 3 Sheets-Sheet 2 Filed Nov. 27, 1959 R m u m I a 5 w. 5.0 m 8 a m 0 R4 6 70 m 7 m 2 W I m 93 Richard 6. Rll'e BY His A/florney R. C. RIKE BRAKE BOOSTER -Nov. 21, 1961 3 Sheets-Sheet 3 Filed Nov. 27, 1959 INVENTOR. Rich 0/0 C. R/Yre BY His Aflgrney United States Patent Ofiice 3,009,449 Patented Nov. 21, 1961 3,009,449 BRAKE BOOSTER Richard C. Rike, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Fiied Nov. 27, 1959, Ser. No. 855,790 8 Claims. (Cl. 121-41) This invention relates to pressure producing devices adapted for use on motor vehicles to aid the operator of the vehicle in applying the brakes and thereby relieve, to a large extent, the manual effort normally required in applying the brakes.

These pressure producing devices or brake booster units as they are known conventionally in the art, usually consist of a container having a movable Wall structure positioned therein for reciprocable movement in the container, the movable wall structure dividing the container into two compartments, one on each side of the movable wall. One of the compartments is adapted normally to have one pressure value, usually atmospheric pressure therein on one side of the wall. The compartment on the opposite side of the wall is adapted to be exposed to the same pressure value, atmospheric pressure, or to be exposed to a pressure value less than atmosphere, such as the vacuum obtained from the manifold of an engine of a vehicle, to produce thereby a pressure differential on opposite sides of the movable wall that causes the wall to be moved by the higher pressure in the direction of the lower pressure.

The degree of pressure differential on opposite sides of the movable wall is regulated by a control valve operated by the operator of the vehicle that regulates the degree of vacuum or less than atmospheric pressure established at one side of the movable wall. The movable power wall is usually connected with the master cylinder of the hydraulic brake system of the motor vehicle so that when a pressure differential is effective on the movable wall or power wall to produce a power movement of the wall, the power wall moves the master cylinder piston under action of the higher pressure applied to the movable wall to displace hydraulic fluid from the master cylinder into the hydraulic brake system and thence into the wheel cylinders to apply the hydraulic brakes of the vehicle under the power effect of the movable wall of the pressure producing device.

The degree of pressure differential established on opposite sides of the movable wall or power wall is regulated by the operator of the vehicle in accordance with the degree of braking effort desired by the operator and the amount of movement of the brake pedal. The movement of the brake pedal actuates the control valve of the pressure producing device in a manner to control the degree of pressure reduction on one side of the power wall of the pressure producing device and thereby control the pressure differential effective on the power wall and the value of the power effort applied into the brake effort for displacing hydraulic fluid into the brake system of the vehicle.

The pressure producing devices or brake boosters, as conventionally provided, on the commercial market are also arranged so that if the pressure producing device should fail to operate for any reason, the master cylinder piston will be actuated by direct manual operation through a direct mechanical connection with the brake pedal of the vehicle.

Pressure producing devices, or brake boosters, that are used conventionally on motor vehicles are also constructed and arranged with mechanism adapted to transmit a brake reaction effect to the foot of the operator so that the operator obtains a feel of physically applying the brakes of the vehicle. The reaction effect transmitted through the reaction means of the pressure producing device operates against the physical force applied by the operator of the vehicle through the brake pedal with the result that this opposing reaction force working against the physical force applied by the operator gives the operator a feel of applying the brakes. The reaction mechanism is constructed and arranged so that only a part of the actual brake applying force is transmitted to the foot of the operator as brake feel in a predetermined proportion to the actual brake pressure.

The reaction force produced while the master cylinder piston displaces hydraulic fluid from the master cylinder is partially transmitted to the movable wall or power wall of the pressure producing device or to some stationary part of the device, only a predetermined portion of the reaction effect being transmitted to the valve control member of the pressure producing device and thereby to the foot of the operator. The operator therefore feels only a small portion of the total reaction effect with the result the physical force of applying the brakes by the operator is greatly reduced, and the full effect of power operation of the pressure producing device is utilized in applying the brakes.

There has been continuous development efforts in pressure producing devices or brake boosters for use on passenger vehicles in applying the brakes of the vehicle Whereby effort on the part of the operator of the vehicle is reduced in applying the brakes, particularly in that portion of the applying stroke in the initial movement of the brake pedal wherein the brake shoes are brought into contact with the brake drum to give the operator of the vehicle a soft pedal feel, at least until the power effect of the pressure producing device is available for power actuation of the master cylinder piston.

It has been considered undesirable during the initial stage of movement of the brake pedal for the operator to have -a substantial fee of brake effort, because during the initial brake pedal movement, the brake shoes are only being moved into engagement with the brake drum with no actual brake effort occurring at the brakes. Any substantial reaction or opposing force applied to the foot of the operator during this initial portion of the brake operation gives the operator a false feel of brake application.

It is the desire of the designers of brake boosters for brake systems on passenger vehicles, trucks and buses to give the operator of the vehicle a light or soft brake pedal feel during the initial movement of the brake pedal, at least until the control valve of the pressure producing device has been moved sufficiently in response to the brake pedal movement as to establish an initial pressure differential on opposite sides of the power wall, whereupon power movement of the master cylinder piston by the power wall of the pressure producing device can take over the major portion of the effort in applying the brakes of the vehicle.

Efforts to provide the operator of the vehicle with a soft pedal during the initial application of the brake of the vehicle has resulted, in some instances, of completely preventing any reaction effect from being applied against the foot of the operator or opposing the operators physical force during the initial stage of operation of the brake pedal and to allow reaction force to reach the foot of the operator for imparting brake feel only after a positive pressure differential is applied to opposite sides of the power wall of the pressure producing device, thereby placing the master cylinder piston under control of the power wall. Such arrangements can result in such free movement of the brake pedal that the operator obtains a feel of a completely free-swinging brake pedal resulting in loss of confidence in the brake system, unless such devices are very carefully engineered and designed. Even then, subsequent adjustment of the brakes can develop the same fault. 7

It is, therefore, an object of this invention to provide a pressure producing device to aid the physical force of the operator of the vehicle to apply the brakes wherein the reaction system for the device is effective at all times in the full brake applying stroke of the device to transmit reaction force or reaction effect to the foot of the operator at a controlled ratio wherein the major part of the available reaction effect is transmitted to the movable wall or a stationary part of the device and only a small portion of the reaction effect is transmitted to the foot of the operator; and wherein, as the reaction effect or force increases during continued application of the brakes, the ratio of the reaction force transmitted to the foot of the operator is changed or varied to increase the proportion of the reaction effect transmitted to the foot of the operator until a predetermined maximum ratio is reached for transmission of the reaction effect between the power wall of the device and the foot of the operator.

The arrangement is, therefore, such as to provide for a small reaction effect or force being transmitted to the foot of the operator during the initial portion of the brake applying stroke to provide a small feel at the brake pedal that the operator will know the brake shoes are being moved into engagement with the brake drum, and as soon as the power effect is available at the power wall, the ratio of the reaction effect transmitted tothe foot of the operator will be increased to its predetermined maximum value that the operator will obtain a brake feel eifort more directly in proportion to the actual brake effort during the actual brake applying portion of the stroke.

It is another object of the invention to provide a pressure producing device or brake booster having the features of the foregoing object wherein the reaction system for the device is arranged to provide for a gradual transition between one relatively low ratio of transmission of reaction effect to the foot of the operator and a second higher ratio to give the operator an increased brake fee the transition being such that the operator does not feel the increasing ratio or increasing reaction effect except as a gradual increase in force opposing movement of the brake pedal.

It is another object of the invention to provide a pressure producing device to aid the physical force of the operator of the vehicle to apply the brakes wherein the reaction system for the device is effective at all times in the full brake applying stroke of the device to transmit reaction force or reaction effect to the foot of the operator at a controlled ratio wherein the major part of the available reaction effect is transmitted to the movable wall or a stationary part of the device and only a portion of the reaction effect is transmitted to the foot of the operator; the reaction system being constructed and arranged in a manner to establish a predetermined ratio for division of the reaction force to the movable wall or a stationary part of the device and to the foot of the operator, the reaction system being in the form of a mechanical leverage system that establishes a predetermined ratio for division of the reaction force between the movable wall and the foot of the operator; the reaction system of this invention including a resilient member placed between the mechanical lever system forming the reaction system and the movable wall or the stationary part of the device which is deformed by the movement of the mechanical reaction lever system in a manner to change the effective pivot connection between the mechanical levers and the support for. the same to change the proportion of the reaction effect to increase the proportion transmitted to the foot of the operator until a predetermined maximum ratio is reached at which the mechanical lever system will thereafter maintain a division of reaction effect between the power wall of the device and the foot of the operator at a relatively constant level but in proportion to the increase of brake effort produced during a brake operation.

Furthen objects and advantages of the present inven tion will be apparent from the following description, reference being had to the accompanying drawings wherein preferred embodiments of the present invention are clearly shown.

In the drawings:

FIG. 1 is a vertical cross-sectional view of a pressure producing device or brake booster incorporating features of this invention.

FIG. 2 is an enlarged cross-sectional view of a part of the pressure-producing device particularly illustrating the reaction system with the members of the reaction system shown in position immediately following the initiation of the power stroke of the movable wall of the pressureproducing device.

FIG. 3 is a cross-sectional view similar to FIG. 2 but illustrating the reaction system in position for maximum transfer of reaction effect to the control member of the device.

FIG. 4 is an elevational view of the power wall illustrating the positioning of the reaction levers of the reaction lever system.

in this invention the pressure producing device or brake booster consists of a cylindrical cup-shaped member 10 having the cylindrical annular wall 11 and a stationary bottom wall 12 as a continuous part of the member 10. A movable wall or power wall 15 is positioned within the cylindrical member 10 and consists of a generally annular casting 16 and a sheet metal cupshaped member 17 having an annular outer flange 18 and an inner annular flange 19. The cup-shaped member 17 is secured to the casting member 16 by means of suitable bolts 29. A generally cylindrical cup-shaped member 21 closes the open end of the member 10 and consists of an annular flange 22 that terminates in a radial flange 23 that locks in engagement with the annular flange 24 on the member 10 by means of bayonet locking members 25. The closure member 21 also consists of an axially extending annular wall 26 that terminates in a radially extending wall 27 that terminates in an opening 28.

A diaphragm member 30, which has a cylindrical form when in the relaxed or noninstalled position in the brake booster, has one end 31 thereof secured between the cup-shaped member 17 and the casting wall 16 to form a fluid seal arrangement and secure the diaphragm to the movable wall 15. The diaphragm 30 follows generally the contour of the cup-shaped member 17 and returns upon itself from the looped end 32 with the portion 33 of the diaphragm lying against the inside wall of the annular portion 11 of the member 10, the wall portion 33 of the diaphragm terminating in an enlarged portion 35 that is retained between the annular flange 24 and the annular flange 22 and locked in position by the bayonet locking members 25 to seal the interior of the pressure producing device against leakage.

The pressure movable wall or power wall 15 divides the housing or container formed by the members 10 and 21 into two chambers A and B, the chamber A being continuously connected with atmosphere through the air inlet connection 36 provided in the wall portion 27 of the member 21. The chamber B is adapted to be exposed to atmospheric pressure or to a pressure below atmosphere, such as that received from the manifold of a motor vehicle on which the brake booster is installed, so that when the chamber B is exposed to the low-pressure source, or vacuum source, there will be a pressure differential created at opposite sides of the pressure wall or power wall 15, the higher atmospheric pressure existing in chamber A and the lower pressure existing in chamber B whereby the power wall is urged to move in a lefthand direction, as viewed in FIG. 1, when the pressure differential exists on opposite sides of the power wall 15.

The casting member 16 of the power wall has an axially extending projection 40 integral therewith forming a hollow chamber that receives an operator operated control valve 50 and a reaction device or mechanism 60. The operator operated control valve 50 regulates the degree of pressure differential existing on opposite sides of the diaphragm by controlling the degree of low pressure or vacuum supplied to the chamber B through the valve control structure in a manner hereinafter described.

The reaction device or mechanism 60 controls proportioning of reaction pressure received from the master cylinder of the brake system between the power wall 15 and the operator operated control valve 50 so as to proportion the reaction effect created in the master cylinder for transmission to the power movable wall 15 and to the control valve 50 and thereby to the foot of the operator to transmit a controlled proportion of the reaction eifect as brake feel from the brake system, all of which is hereinafter more fully described.

The wall portion 12 of the cylindrical member 10 carries a master cylinder 70 and a reservoir 71 for the master cylinder. The reservoir and master cylinder are secured to the stationary wall 12 by means of the bolts or stud fasteners 72. The master cylinder 70 has an annular bore 73 in which the master cylinder piston 74 reciprocates. The master cylinder piston 74 has the end portion 75 that extends into the chamber B of the pressure producing device or brake booster. The master cylinder piston, consisting of the forward end portion 74 and the rear end portion 75, is journaled in the master cylinder 73 and in the bearing portion 76 that extends rearwardly from the reservoir and master cylinder casting. Suitable annular seals 77 are provided between the portion 75 of the master cylinder piston and the hearing portion 76 to prevent loss of hydraulic fluid from the master cylinder 73 into the brake booster chamber B, and also prevent air pressure or vacuum from entering the master cylinder.

The master cylinder piston 74 has a cup seal 80 on the forward end thereof engaging the cylinder bore 73, and when in the fully retracted position, as shown in FIG. 1, the forward edge of the cup seal is rearwardly of the port 81 that connects the master cylinder 73 with the reservoir 71. Thus, when the master cylinder piston is in fully retracted position, when the brakes are released, the master cylinder 73 is under the same atmospheric pressure as the reservoir chamber 71, a suitable vent port (not shown) being provided in the filler cap 82 for the reservoir. A conventional residual pressure check valve (not shown) is provided in the forward end of the master cylinder 73 to allow displacement of the hydraulic fluid from the master cylinder into the brake lines 83 when the master cylinder piston 74 is moved in a left-hand direction, either under control of the pressure producing device or under direct manual control in a manner hereinafter described. The check valve provided in the forward end of the master cylinder 73 also allows return of the brake fluid from the brake lines 83 back into the master cylinder in convenitonal manner and thence into the reservoir 71 when the brakes are allowed to move to retracted position, but conventionally provides for retention of a small residual pressure in the brake lines 83 to prevent any possibility of air entering the brake lines. A compression spring 84 placed within the master cylinder has one end engaging the cup seal 80 on the forward end of the master cylinder piston 74 and has the opposite end engaging the residual pressure check Valve in the forward end of the master cylinder to urge the piston 74 into its retracted position, as shown in FIG. 1, when the brake pedal is released by the operator of the vehicle. Passages are provided in the master cylinder piston connecting the chamber 86 around the master cylinder piston with the port 87 in the bottom wall of the reservoir to prevent cavitation in the master cylinder 73 on sudden retraction of the piston 74 in a right-hand direction on release of the brake pedal by the operator.

The extension portion of the master cylinder 74 that projects into the chamber B of the pressure producing device has an axial bore 90 that slidably receives the forward end 91 of the manually operable control member 50. The control member 50 has an axial bore 92 that receives the actuating rod 93 that projects exteriorly of the pressure producing device and has the connection 94- on the end thereof by which the actuating rod is connected to the brake pedal system of the vehicle for direct actuation by the operator. The forward end of the actuating rod 93 has a spherical element 95 received within a retaining member '96 for holding the actuating rod within the bore 92 in the manually operable control member 50. The control member 50 also forms a valve element for controlling the degree of low pressure or vacuum supplied to the chamber B of the pressure producing device. The forward end of the bore 90 in the extension element 75 of the master cylinder has a rubber bumper 97 that may be engaged by the forward end of the control member 50- for direct and positive manual operation of the master cylinder piston 74 in the event the pressure producing device or brake booster should fail to operate for any reason.

The operator operated control member 50 consists of a valve element 100* that has an annular valve seat 101 on the forward face thereof. The valve element 100 operates Within a chamber 102 provided in the extension portion 40 of the casting member 16. The forward end of the wall forming the chamber 102 has a valve seat 103 on which a valve element 105 is adapted to seat when the device is in the position illustrated in FIG. 1. Also, as illustrated in FIG. 1 the seat 101 is disengaged from the valve element 105 when the brake booster is in retracted position.

The valve element 105 also includes a radially extending diaphragm supporting flange 106 that seats within the recess 107 in the extension 40 of the casting element 16.

The diaphragm portion 106 of the valve element 105, together with the valve element 105 seating on the seat 103, forms an annular chamber 110 around the periphery of the valve element 105 but which is closed or sealed off from the chamber 102 when the valve member 105 is in the position illustrated in FIG. 1.

The chamber 110 has an inlet connection 111 connected with a flexible pipe line 112 that, in turn, is connected with the manifold of the vehicle on which the device is installed to provide a low-pressure source or vacuum source for supply to the chamber 110. The connection of the manifold of the engine with the chamber 110 will maintain the chamber constantly at low-pressure value or at vacuum value depending upon the value of the low pressure in the manifold of the engine.

The rearward end portion 115 of the master cylinder plunger has a sliding fit with the annular flange 19 of the cup-shaped member 17 and carries a radial member 116 in the form of a disk that has the peripheral portion thereof formed arcuately to form an annular seat 117 forming a pivot axis.

A plurality of levers 121 are pivotally supported on the casting element 16 in the manner illustrated in FIGS. 2 and 4.

Each of these lever members 121 is in the form of a T-shaped element with the end portions 122 being re ceived in recesses 123 in the casting element 1 6, the ledge portion 123a providing the fulcrum whereby the lever members 121 are pivtally supported on the casting element 16. The stem portion 124 of the lever members 121 extends toward the axis of the device, as shown in FIGS. 1 and 4.

The inner ends of the stem portions 124 of the levers 121 engage a reaction disk member 126 that is slidably carried on the plunger portion 91 of the operator operated control member 50.

A compression spring 127 extends between the reaction disk member 126 and the valve element 160 of the operator operated control member 50 and a second compression spring 128 extends between the disk 126 and the valve element 105. The compression spring 127 retains the control member 50 in the position illustrated in FIG. 1 with the seat 101 disengaged from the valve element 105 when the brake booster or pressure producing device is in inactive or retracted position. The spring 128 retains the valve element 105 on the seat 103 and thereby closes the chamber 110 against connection with the internal chambers of the pressure producing device.

The springs 127 and 128 also operate to retain the disk member 126 normally out of engagement with the shoulder 130 formed on the extension portion 91 of the operator operated control member 50 and between the forward end portion thereof and the valve element portion 100, and are therefore in the reaction system for transmitting reaction effect to the control member 50 whenever pressure is produced in the master cylinder 73. As shown on the drawings, the position of the reaction levers 121 on the power wall provides a chamber 141 in the general form of an annulus around the previously described valve assembly. An annulus or endless ring of elastomeric material or rubber-like material 200 is placed in the chamber 141 between the inner side 201 of the reaction levers 121 and the face 202 of the chamber 14.

When the brake booster is in the inactive or released position, as shown in FIG. 1, the annulus of elastomeric material 200 spans the axial dimension of the chamber 141 between the reaction levers 121 and the face 202 of the chamber 141 and is just sufficiently larger in diameter that positioning of the resilient annulus of elastomeric material 200 in the position shown in the drawings will provide a fulcrum for the reaction levers 121 that is radially inside of their fulcrum on the power wall 15. At this time the levers 121 are not in engagement with the mechanical fulcrum 12311 for the levers 121 on the power wall. The closely adjacent positions of the pivot axis 117 and the fulcrum formed by the resilient ring 200 provides the highest mechanical advantage for transfer of a major portion of reaction effect to the power wall 15 and a minor portion to the foot of the operator as brake feel to thereby give a soft initial pedal feel.

As the brake booster moves through a power stroke during a brake application to shift the position of the reaction levers 121 from that position shown in FIG. 1 to that shown in FIG. 2 and thence to that in FIG. 3, the annulus of elastomeric material 200 will be compressed or deformed by a decrease of axial distance between the mechanical levers 121 and the face 202 of the chamber 141. This deformation of the resilient annulus 200 by the reaction levers 121 results in a shift in the fulcrum of the levers 121 from the annulus 200 to the fulcrum 123a on the power wall 15 whereby to reduce the mechanical advantage and increase the proportion of reaction effect transmitted to the foot of the operator.

Specifically, when the mechanical levers 121 are in the position shown in FIG. 1, the fulcrum for the levers 121 is on the resilient annulus 200, the outer ends of the levers being spaced from the fulcrum 123a on the power wall. But as the levers 121 shift their position from that shown in FIG. 1 to that shown in FIG. 2 and thence to FIG. 3, the fulcrum for the levers 121 will shift radially outwardly on compression of the annulus 200 until the outer ends of the levers 121 fulcrum on the power wall at 123a. Thus, the shifting of the fulcrum of the levers 121 radially outwardly from their initial point of fulcrum on annulus 200 will decrease mechanical advantage and increase the proportion of reaction effect that is transmitted to the control member and thereby to the foot of the operator as the brake booster moves through a brake applying stroke.

With the elements of the pressure producing device in the position illustrated in FIG. 1, which is the retracted or inactive position, chambers A and B will both be at atmospheric pressure with chamber A receiving its air through the inlet connection 36. Chamber B is connected with chamber A at this time through the port 140, annular chamber 141, through the clearance provided in the opening 142 in the valve element 105 and thence between the seat 101 and the valve element 105 and chamber 102 which connects with the port 143 and chamber B. At this time therefore both chambers A and B are under the same atmospheric pressure so that the return spring 145 provided between the wall 12 and the movable wall 15 retains the movable wall 15 in the position shown with the resilient stop nubs 146 engaging the radial wall portion 147 of the closure member 21.

A rubber seal member 150 is provided between the end portion 151 of the manually operated control member 50 and the end of the casting extrusion 40 to prevent air from entering the chamber 102 when the chamber is under low pressure or vacuum conditions in a manner hereinafter described. A rubber dirt cover member 152 is provided between the manual control rod 93 and the wall 21 of the brake device.

Under conditions just previously mentioned with atmospheric pressure existing in chambers A and B through the passages heretofore outlined, low pressure or vacuum is retained in the chamber 110 that is connected with the vacuum source consisting of the manifold of the engine of the vehicle.

Referring to the several figures of the drawings and disregarding the resilient annulus 200, the operation of the device is as follows.

When the operator of the vehicle begins a brake application the first minute movement of the brake pedal under control of the foot of the operator moves the actuating rod 93 in a left-hand direction, as viewed in the several figures, a sufficient distance to cause the seat 101 on the valve member to engage the seat element a of the valve element 105. At this time spring 127 is the only force opposing the movement of the member 50 by the operator. The manually operated control member 50 is freely slid-able in the bore 90 of the master cylinder piston end portion 75. However, under this operation the left hand end of the plunger extension 91 of the valve member 50 will not engage the bumper member 97, this engagement being reserved for failure of the power device.

This initial leftward movement of the manually operated control member 50, to effect engagement of the valve seat 101 with the seat element 105a, will not cause any movement of the master cylinder piston 74 because the compression force of the spring 84 is suflicient to retain the piston 74 in the position illustrated in FIG. 1, and the sliding friction between the member 91 and the end portion 75 of the master cylinder piston is insuflicient to overcome the force effect of the spring 84.

At the time the seat 101 on the manually operated control member 50 engages the seat element 105, connection of chamber B with chamber A is broken by this valve closing engagement so that chamber 102 is now isolated from chamber A While it is still in connection with chamber B through port 143.

A slight additional movement of the control member 50 by the operator of the vehicle moves the manually operated member 50 in a slightly further left-hand direction until the seat element 105 is lifted from the seat 103 on the casting member 16 as shown in FIG. 2. When this occurs the low pressure or vacuum existing in chamber is connected with the chamber B of the brake booster through the clearance between the seat 103 and the valve seat element 105a, this clearance passage being connected with the chamber 102 and it, in turn, with the chamber B through the port passage 143.

As soon as low pressure or vacuum is available to chamber B for withdrawing atmospheric air from this chamber and reducing its pressure, a pressure differential is established between chambers A and B with the atmospheric pressure in chamber A urging the power wall or movable wall of the brake booster in a left-hand direction aaginst the action of the spring 145.

Initial movement of the power wall 15 in a left-hand direction causes left-hand movement of the master cylinder piston 74- because of the mechanical connection made between the master cylinder piston and the power wall 15 through the valve element 165, the springs 12% and 127, and the reaction system 61), with the result the forward end 86a of the cup seal 80 on the master cylinder piston 74 moves toward the port 81 between the master cylinder 73 and the reservoir until this port is closed.

During the initial portion of the applying stroke just mentioned, in which the valve element 199 seats upon the valve element 1115 and valve element 105 lifts from the seat 1113 and the master cylinder piston moves forward to close the port 81, no hydraulic pressure is developed in the master cylinder 73 because the port 81 is fully open so that any fluid displaced from the master cylinder piston will pass through the port 81 into the reservoir to maintain the master cylinder under atmospheric pressure.

However, during that portion of the initial applying stroke following the slight opening of the vacuum passage between valve element 105a and the valve seat 103, the pressure differential established between chambers A and B is sufficient to overcome the effect of the retraction spring 145 in the brake booster and, together with the foot applied effort on member 50, overcomes the retraction spring 84 in the master cylinder so that the forward movement of the master cylinder piston to close port 81 is under the power effect of the power wall 15 and the foot effort of the operator applied to member 50. Thus the operator of the vehicle does not feel this initial movement of the master cylinder piston to close port 81 during the portion of the applying stroke because the force effect of spring 84 is not sufiicient to overcome the force effect of springs 127 and 128 at this time. All the operator has felt thus far is the force of the light spring 127 when closing valve seat 101 onto the valve element 105a and of spring 128 on lifting valve element 105 from its seat 103.

However, when the port 81 in the master cylinder 73 is closed by the forward lip of the lip seal 80 on the master cylinder piston 74, hydraulic pressure will 'be developed in the master cylinder 73 on continued leftward movement of the piston 74- under action of the power wall 15 with the result the pressure increases internally in the master cylinder to displace the hydraulic fluid into the brake system to move the brake shoes into engagement with the brake drum, this being the purpose of initial displacement of hydraulic fluid from the master cylinder into the brake lines and the wheel cylinders of the hydraulic brake system on the vehicle.

When hydraulic pressure increases in the master cylinder 73, a counter force effect tends to urge the master cylinder piston in a right-hand direction against the action of the power wall 15. When this occurs this counter force effector reaction effect is transmitted rearwardly through the master cylinder piston extension 75 to the disk member 116 or reaction disk as it can be referred to herein. This reaction disk 116 engages the levers 121 at a point radially inwardly of their pivot axis 123a on the casting member 16 with the result the reaction force or reaction effect transmitted by the disk 116 is divided proportionately between the power wall 15 and the reaction disk 126 carried on the member 91. The reaction force is therefore proportioned between the power wall 15 and the reaction element 126 so that only a part of the reaction effect is transmitted through the springs 127 and 128 to the manually operated control member 50 to be felt by the operator as brake applying feel or pressure. The initial reaction force thus transmitted to the control member 50 in this initial portion of the brake applying stroke is not sufiicient to move reaction disk 126 against the compression force of springs 127 and 128.

As soon as the value of the reaction force, or proportion of reaction force, transmitted by the levers 121 through the reaction disk 126 is equivalent to and slightly exceeds the force effect of the springs 127 and 128, the reaction levers 121 will move gradually in a righthand or counterclockwise direction about their pivot axis on the casting element 16 as the reaction effect increases to thereby move the reaction disk 126 in a right-hand direction, as viewed in the respective figures, against the compression of the springs 127 and 128 that are both now being supported by the valve member which, in turn, is supported by the foot of the operator by means of its connection through the applying rod 93 that is connected to the brake pedal of the vehicle. Thus, any reaction force created or which is the result of hydraulic pressure developing in the master cylinder 73 is transmitted to the foot of the operator of the vehicle as brake feel as soon as any hydraulic pressure overcomes the force effect of the springs 127 and 128.

As soon as the initial reaction force or effect overcomes the force effect of springs 127 and 128 there is produced initial movement of the reaction disk 116, the levers 121 and the reaction disk 126 moving to their positions illustrated in FIG. 2.

As the reaction effect increases as a result of increase of hydraulic force in the master cylinder 73 produced by an increase of the force required in brake application, the force value of the reaction effect transmitted to the reaction disk 126 in the manner heretofore described will further compress the springs 127 and 128 until the reaction disk 126 engages the shoulder 130 on the plunger member 91, as shown in FIG. 3. The result is that the initial reaction effect transmitted as brake feel to the foot of the operator is resiliently taken by the springs 127 and 128, and, as soon as the reaction force is sufficient to overcome the effect of the springs 127 and 128, the reaction effect is then positively mechanically transmitted to the member 91 through the connection between the reaction disk 126 engaging the shoulder 130 as a predetermined proportion of the total reaction effect. At this time the operator of the vehicle is receiving reaction effect from the master cylinder piston in a predetermined direct proportion to the force required to apply the brakes and in direct proportion to the pressure differential on opposite sides of the power wall 15, and also thereby in direct proportion to the pressure value in the chamber B as controlled by the manually operated control member 50.

Referring now to the action of the resilient annulus 200 placed between the reaction levers 121 and the surface 202 of the chamber 141 which modifies the operation just described in the following manner.

The resilient annulus 200 is adapted to provide for a change in the mechanical ratio or proportioning of the reaction effect between the power wall 15 and the control member 50 during the brake applying stroke so that at the start of the first part of the applying stroke the mechanical advanage of the reaction system is high with the result that a major portion of any reaction effect is transmitted to the power wall 15, only a small portion of the reaction effect being transmitted to the foot of the operator as brake feel through the reaction disk and the springs 127 and 128. During this initial part of the applying stroke the reaction levers 121 engage the annulus 200 as the fulcrum to obtain the major mechanical advantage of the reaction lever system for transfer of reaction effect to the power wall. This sof reaction feel is desired to be retained in the brake applying stroke until the brake shoes are in engagement with the break drums, after which the actual brake applying force is developed.

After the control member 50 has moved the valve a to the position shown in FIG. 2, at which the power wall 15 will be under the effect of pressure differential between chambers A and B to place the brake booster on a power stroke, the mechanical advantage of the reaction system can be changed gradually over a transition period to increase the proportion of the reaction effect transmitted to the control member 50 to more nearly approach the actual brake applying force and increase proportionately the reaction feel transmitted to the foot of the operator of the vehicle.

As hydraulic force increases within the master cylinder 73 with resultant reaction effect being transmitted from the master cylinder piston 74 to the reaction disk 116 and thereby to the reaction levers 121, the resilient annulus 200 will be compressed or deformed so that the fulcrum of the levers 121 will shift from the fulcrum formed by the annulus 200 to the fulcrum 123a that is positioned radially outwardly of the annulus 200. This results in a reduction in the mechanical ratio for proportioning reaction effect to the power wall 15 with a resultant increase to the control member 50 to increase the proportion of the reaction effect transmitted to the foot of the operator as brake feel. Also the resilient annulus 230 having a desired degree of resilience will provide for a gradual transition of the change in proportion of reaction effect transmitted to the foot of the operator so that increase of proportion of reactin effect transmitted to the control member 50 will be felt by the operator merely as an increased brake force with no sharp transition at any point until the full mechanical advantage is obtained for transmissions of reaction effect with the reaction system assuming the position shown in FIG. 3 whereat the proportioning effect will remain relatively constant during the major portion of the brake applying stroke but will gradually increase the force effect on the foot of the operator as brake feel.

From the foregoing description it will be apparent that reaction feel is transmitted from the master cylinder piston to the foot of the operator of the vehicle as brake feel whenever reaction effect is available for transmission from the master cylinder, and that the reaction effect is transmitted in one proportion or mechanical ratio during the initial brake applying stroke to provide a low proportion of reaction effect transmitted to the foot of the operator, which ratio or mechanical advantage is gradually changed to a predetermined ratio or mechanical advantage for increasing the proportion of the reaction effect transmitted as brake feel, the transition being under control of a resilient member that avoids any feel of sharp transition from one ratio to another.

While the embodiments of the present invention as herein disclosed constitute a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. A brake booster for applying a brake of a vehicle in which physical force of an operator is supplemented by power assistance, comprising, a power cylinder, a pressure responsive movable wall in the power cylinder, a reaction means arranged to exert a reaction force varying with variations in the force exerted by the movable wall, an operator operated control member actuated by physical force of an operator to control the operation of the movable wall, said control member being urged against the physical force of the operator by the reaction means, and an annulus ring of elastomeric material compressible between said reaction means and said movable wall forming a resiliently acting ratio changing force transmitting means between said reaction means and said movable wall effective with said reaction means in transmitting at least a part of the reaction force to the control member in a changing ratio during a brake applying stroke of the brake booster, initial compressibility of said member between said reaction means and said movable wall opposing a shift in force transmission ratio to the control member during an initial portion of the brake applying stroke.

2. A brake booster for applying a brake of a vehicle in which physical force of an operator is supplemented by power assistance, comprising, a power cylinder, a pressure responsive movable wall in the power cylinder, a reaction means arranged to exert a reaction force varying with variations in the force exerted by the movable wall, an operator operated control member actuated by physical force of an operator to control the operation of the movable wall, said control member being urged against the physical force of the operator by the reaction means, and an annulus ring of elastomeric material compressible between said reaction means and said movable wall forming a resiliently acting ratio changing force transmitting means between said reaction means and said movable wall effective with said reaction means in transmitting at least a part of the reaction force to the control member in a changing ratio during a brake applying stroke of the brake booster after a predetermined reaction force is reached during the brake applying stroke.

3. A brake booster for applying a brake of a vehicle in which physical force of an operator is supplemented by power assistance, comprising, a power cylinder, at pressure responsive movable wall in the power cylinder, a reaction means arranged to exert a reaction force varying with variations in the force exerted by the movable wall, an operator operated control member actuated by physical force of an operator to control operation of the movable wall, said control member being urged against the physical force of the operator by the reaction means, and a member of elastomeric material compressible between said reaction means and said movable wall forming a resiliently acting ratio changing force transmitting means between said reaction means and said movable wall effective with said reaction means in transmitting at least a part of the reaction force to the control member in a changing ratio during a brake applying stroke of the brake booster, initial compressibility of said member between said reaction means and said movable wall opposing a shift in force transmission ratio to the control member during an initial portion of the brake applying stroke, compression of said member between said reaction means and said movable wall effecting radial elongation of said member to change thereby the ratio of division of the force transmission between said movable wall and said control member.

4. A brake booster for applying a brake of a vehicle in which physical force of an operator is supplemented by power assistance, comprising, a power cylinder, a pressure responsive movable wall in the power cylinder, a reaction means arranged to exert a reaction force varying with variations in the force exerted by the movable wall, an operator operated control member actuated by physical force of an operator to control the operation of the movable wall, said control member being urged against the physical force of the operator by the reaction means, and a member of elastomeric material compressibie between said reaction means and said movable wall forming a resiliently acting ratio changing force transmitting means between said reaction means and said movable wall effective with said reaction means in transmitting at least a part of the reaction force to the control member in a changing ratio during a brake applying stroke of the brake booster, initial compressibility of said member between said reaction means and said movable wall opposing a shift in force transmission ratio to the control member during an initial portion of the brake applying stroke, said member being retained between said reaction means and said movable wall in a manner to prevent movement of the body of the said member radially outwardly relative to the axis of the brake booster, compression of said member between said reaction means and said movable wall during the brake applying stroke causing radial elongation of said member in a direction radially inwardly toward the axis of the brake booster to effect thereby a change in the ratio of division of force transmission between said movable wall and said control member.

5. A brake booster for applying a brake of a vehicle in which physical force of an operator is supplemented by power assistance, comprising, a power cylinder, a pressure responsive movable wall in the power cylinder, reaction means comprising lever means arranged to exert a reaction force varying with variations in the force exerted by the movable wall and proportion the reaction force between said movable wall and an operator operated control member actuated by physical force of an operator to control the operation of the movable wall, said control member being urged against the physical force of the operator by said reaction means, an annulus ring of elastomeric material compressible between said lever means and said movable wall, compression of said elastomeric member by movement of said lever means relative to said movable wall effecting change in the pivotal relationship of said lever means relative to said movable wall and change thereby the proportion of the reaction force transmitted to said control member during a brake applying stroke of the brake booster.

6. A brake booster for applying a brake of a vehicle in which physical force of an operator is supplemented by power assistance, comprising, a power cylinder, a pressure responsive movable wall in the power cylinder, reaction means comprising lever means pivotally supported on the movable wall to exert a reaction force varying with variations in the force exerted by the movable wall and proportion the reaction force between said movable wall and an operator operated control member in a fixed and predetermined proportion, said operator operated control member being actuated by the physical force of an operator to control the operation of the movable wall, said control member being urged against the physical force of the operator by said reaction means, a member of elastomeric material positioned radially inwardly of the pivot support for said lever means and compressible between said lever means and said movable wall, compression of said elastomeric member by movement of said lever means relative to said movable wall effecting change in the pivotal relationship of said lever means relative to said movable wall and change thereby the proportion of the reaction force transmitted to said control member during a brake applying stroke of the brake booster.

7. A brake booster for applying a brake of a vehicle in which physical force of an operator is supplemented by power assistance, comprising, a power cylinder, a pressure responsive movable wall in the power cylinder, reaction means comprising lever means having fulcrum means on said movable wall and arranged to exert a reaction force varying with variations in the force exerted by the movable wall and proportion the reaction force between said movable wall and an operator operated control member actuated by the physical force of an operator, said operator operated control member controlling the operation of the movable wall, said control member being urged against the physical force of the operator by the reaction means, a member of elastomeric material positioned between said reaction lever means and said movable wall radially inwardly of the said fulcrum of said lever means on said movable wall relative to the axis of the brake booster and compressible by movement of said lever means relative to said movable wall to efifect thereby a change in the fulcrum of said lever means from said elastomeric member to said first-mentioned fulcrum and increase thereby the proportion of the reaction force applied to said control member.

8. A brake booster for applying a brake of a vehicle in which physical force of an operator is supplemented by power assistance comprising, a power cylinder, a pressure responsive movable wall in the power cylinder, reaction means comprising lever means having fulcrum means on said movable wall and arranged to exert a reaction force varying with variations in the force exerted by the movable wall and proportion the reaction force between said movable wall and an operator operated control member actuated by physical force of an operator, said operator operated control member controlling the operation of the movable wall, said control member being urged against the physical force of the operator by the reaction means, a member of elastomeric material positioned between said reaction lever means and said movable wall radially inwardly of the said fulcrum of said lever means on said movable wall relative to the axis of the brake booster and compressible by movement of said lever means relative to said movable wall to effect thereby a change in the fulcrum of said lever means from said elastomeric member to said first-mentioned fulcrum and change thereby the proportion of the reaction force applied to said movable wall and to said control member, said compression of said elastomeric member changing the said fulcrum to etfect an increase in the reaction force transmitted to said control member.

References Cited in the file of this patent UNITED STATES PATENTS 2,826,042 Rike et al Mar. 11, 1958 2,828,719 Ayers Apr. 1, 1958 2,867,193 Ayers Jan. 6, 1959 

